Compile Error

Sincerely,
I have a problem:
I have spent a web project, but I have spent Proyecto.war
decompile when the entire project I have not had any problems.
But there is a class that has come out with this name: ProyectoMejoraController$ModalEstBean.class
It is okay to name but the $.
I want to know which means the $ to change its name and that normal without this symbol.
sorry for writing
Greetings from PERU.